Light-activated diazography

ABSTRACT

A light-activatable, thermally developable diazosulfonate reproduction material and methods of imaging same.

United States Patent 1 1 11 1 3,713,825 Girard 1451 Jan. 30, 1973 15 41 LIGHT-ACTIVATED DIAZOGRAPHY 3,309,200 3/1967 B erman..:...... .96/49 6 [75] inventor: Eric Lionel Girard, Holyoke, Mass. Khmkowsk' [73] Assignee: The Plastic Coating Corporation, 3,163,401 2/1965 South Hadley, Mass. 2,525,751 10/1950 2,680,062 6/1954 [22] Filed: April 27, 1970 3,191,030 6/1965 2,653,091 9/1953 [21] APPL 32,420 3,331,689 7/1967 Sosnovsky 6181. ..96/49 52 us. 01 ..96/49, 96/27 R, 96/45.2, OTHER PUBLICATIONS 96/91 250/65 Dinaburg, M. S., Photosensitive Diazo Cpds, The [51] Int. Cl ..G03c 5/34,G03c 1/56 Focal p 19 4, 13 17, 4 47, 30433, 93, [58] Field of Search ..96/49.9l, 75; 250/65.1; 123 133 152 154 &1 0

- Kosar, 1., Light-Sensitive Systems, John Wiley &

Sons, 1965, p.266, 269, 270, 278, 291, 314-317. [56] References Cited Prima'ry Examiner-Charles L. Bowers, .lr. UNITED STATES PATENTS Attorney-John A. Weygandt, William J. Foley, Mar- 3,479,l83 11/1969 Habib et al. ..96/75 X tin L. Faigus and John W. Kane, 1r. 1,997,507 4/1935 Akintievsky ..96/91 X 2,854,338 9/1958 Herrick et a1 96 49 x [57] ABSTRACT 2,429,249 10/1947 Von Glahn et a1. 96/49 X 2,217,189 10/1940 Sus ..96/49 A g tthermally developable dlazosul- 2,694,009 11/1954 Sus 96/49 X fonate reproduction material and methods of imaging 2,197,456 4/1940 Von Poser et al. ..96/9l same, 1,926,322 9/1933 Van der Grinten et a1 ..96/91 X 3,312,551 4/1967 Sus ..96/75 9 Claims, N0 Drawings LIGHT-ACTIVATED DIAZOGRAPHY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to photosensitive diazotype materials and to methods using said materials to produce images.

2. Description of the Prior Art Diazotype processes rely upon the light-sensitivity of diazo salts and the fact that the salts undergo two different types of reactions: replacement or decomposition, in which nitrogen is lost as nitrogen gas and some other atom or group becomes attached to the benzene ring in its place; and coupling, wherein the nitrogen of the diazo group is retained and the salts react with certain aromatic compounds to yield products called azo dyes.

The photochemical sensitivity of the compounds typically employed in diazotype photographic reproduction (photoreproduction) materials resides in the near-ultraviolet region of the spectrum, and is centered about 400 nm (nanometers, one am being equal to a millimicron or meter). Photographic diazo processes may be divided into two categories: positiveworking processes and negative-working or reversal, processes. In the former category, the action of light causes photochemical decomposition of the diazo compound. An image is developed in the unexposed areas by the combination of the diazo compound with a coupling component, which is generally an aromatic amine, phenol, phenol ether or aliphatic compound containing active methylene groups, to form colored oxyazo or aminoazo compounds known as azo dyes.

The positive working material is imaged by first exposing it through a master transparency or original. The light in the exposure step must supply sufficient energy to destroy the diazo compound in the areas corresponding to the clear background of the original. High-pressure mercury vapor lamps are generally used in performing this step. That part of the diazo coating which is unprotected from the ultravioletradiation by the image on the original becomes a colorless substance, incapable of coupling to form a dye. But the unaffected diazo compound which remains in those areas where the light has not struck is able to form an azo dye with a coupling component when the medium is made alkaline. Thus, wherever there was an opaque line on the original, a dye-line appears on the copy. Positive-working, diazotype photoreproduction material is generally made alkaline either by impregnating the material with ammonia vapors or passing it through an alkaline developing solution.

, In the negative-working or reversal process, a dye is formed. in the exposed areas, but not in the areas protected from light. Thus a negative, or reversed, copy of the original transparency results. Among the processes employing diazo compounds to produce reversal copies are those employing diazosulfonates. Illustrative thereof is U.S. Pat. No. 2,854,338 issued in 1958 to Herrick et al., wherein a neutral or acid photosensitive material is exposed to actinic light and developed in ammonia vapors. Residual diazosulfonate is removed from the unexposed areas and the background cleared by washing in water. In accordance with a more recent process, disclosed in U.S. Pat. No. 3,479,183 issued Nov. 18, 1969 to Habib et 211., an alkaline imaging cleared by exposing it to overall actinic illumination,

thereby forming colorless decomposition products of v the diazosulfonate to produce a stable, negative dyeimage against a clear background.

A principal disadvantage of conventional diazotype processes has been that development of the image is chemically activated and requires either a vaporous or liquid I developer. The many inconveniences characteristic of this type of processing have led to efforts to find a truly dry diazotype process. All of these efforts have been largely unsuccessful, at least in practice, since they entailed other disadvantages equally as serious as those involved with wet or vaporous processing. In general, attempts to employ the accelerating effect of heat on the coupling reaction could not be utilized in the development of diazotype materials, principally because of the destructive action of heat on the diazo compounds. The diazosulfonates, however, tend to be indifferent toward couplers at room temperature but can be activated by heat.

Between 1940 and 1954, a number of U.S. Pats. Nos.

(e.g., 2,217,189, 2,429,249 and 2,694,009) were.

granted to Sues for a positive-working photographic process wherein paper coated with a solution of a diazosulfonate and a coupling component is first exposed to light for a time sufficient to decompose the diazo compound. An image is then developed by heating the paper to form a dye in the areas which were not exposed to light. Other patents, for example U.S. Pat. No. 3,312,551, have issued relating to reflex thermography, which is the inverse of the above-described photographic Sues process. In the thermographic reflex process, imaging is accomplished by selectively heating the diazosulfonate layer and clearing is performed by overall exposure to light. These processes, however, have not found commercial success, apparently because they lack sufficient photosensitivity and require relatively high temperatures to form the image.

Thus, for more than thirty years, men of extraordinary skill in the diazo art have been looking at diazosulfonate formulations. Those who were investigating positive-working, thermally developable processes, (see, for example, U.S. Pat. No..2,2l7,l89 supra) insisted that the imaging light should destroy the diazosulfonate so that the remaining diazosulfonate could be caused to coupled by the application of heat. Those who were investigating reversal processes (see, for example, U.S. Pat. No. 2,854,338 supra) understood that, for various reasons, heat would not be a desirable developing means. Indeed, as recently as 3 SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a highly photo sensitive diazotype reproduction material, which can be developed and fixed without the application of any chemical.

A further object of the invention is to provide a diazotype photoreproduction process which can be either positive-working or negative-working.

A still further object of the invention is to provide a diazotype thermographic reproduction material.

Contrary to what one of ordinary skill in the art would surmise, the present inventor has discovered that an aryl diazosulfonate, when exposed to light of wavelengths greater than a specific wavelength (designated hereinafter as a first range of wavelengths), is converted to a labile form which is substantially unaffected by light of said wavelengths and is capable of coupling with a coupling component, and that when exposed to light of wavelengths less than said specific wavelength (designated hereinafter as a second range of wavelengths) this labile form decomposes. It has further been found that the rate of the reaction between the labile form and the coupling component can be promoted by heat. Accordingly, the present invention comprises a light-.activatable, thermally developable diazo photoreproduction material and a light-activatable material.

While aryl diazosulfonates as a class are operable in the present invention, the labile form does not appear to be the same for all species. Furthermore, some diazosulfonates exhibit a measurable separation between the absorption maxima of the diazosulfonate form and the photo-generated labile form. Thus, the first range of wavelengths, under the exposure of which such a diazosulfonate is converted to a labile form, consists of wavelengths approximately equal to and greater than the absorption maximum of the diazosulfonate. The second range of wavelengths, under the exposure of which the labile form decomposes, consists of wavelengths approximately equal to and less than the absorption maximum of the labile form. The species showing such separation are preferred for use in the present invention.

Other species exhibit no substantial separation between the first and second ranges. The existence of such a separation, although apparently very slight, is evidenced by the behavior of such latter species. The absorption spectra of the diazosulfonate and the labile form can be measured, even though they may overlap.

The diazosulfonate generally absorbs farther into the visible region,'i.e., at longer wavelengths, than the labile form. When a formulation containing a diazosulfonate which exhibits no substantial spectral separation is subjected to radiation consisting of these longer wavelengths, the labile form which is generated is substantially unaffected by such radiation. When radiation of shorter wavelengths is included in the incident radiation, decomposition of the labile form occurs. The selection of the first range of wavelengths, i.e., the longer wavelengths, and of the second range, i.e., the shorter, is optimized empirically by choosing ranges which maximize the density of the image which results upon heating.

thermographic diazotype,

and greater than the shifted absorption maximum con-'- verts the diazosulfonate to the labile form, which is substantially unaffected by such radiation.

Although it is somewhat anomalous to speak of the pH of a dry layer, since pH expresses the hydronium ion concentration, diazo coatings have long been described in terms of their acidity or alkalinity. Whatever the mechanism, it is well known that acids and bases influence the propensity of diazo compounds to couple. For purposes of the present invention, the pH of the layer is not especially critical to the formation of the labile species or for the development step. In order to satisfactorily clear the material, however, the layer must be acid or neutral, and as used hereinafter,*the term acid is intended to include neutral. While alkaline material can be exposed, developed and then made acid, it is far more convenient and advantageous to start with acidic material. Consequently, in accordance with the preferred embodiment of the present invention, the medium is initially made acid. Acidity stabilizes the components prior to imaging and facilitates clearing. Furthermore, an acid layer can be developed and cleared without the application of any chemical.

When a diazosulfonate of the present invention is exposed to light of a first range of wavelengths, the diazosulfonate in the area struck by light is converted to a labile form. When this labile form is subjected to heat in the presence of a coupler, it combines with the coupling component to form an azo dye. If the labile form is exposed to light of a second range of wavelengths, however, it decomposes. Thus are defined for the photoreproduction processes of the invention the basic steps of exposing to light to form an invisible, undeveloped image, developing the image, and clearing (fixing) the image. These steps permit three modes of copying; two positive working processes and one reversal process.

In accordance with one positive working process, the light sensitive layer is exposed overall to light of a first range of wavelengths, thereby converting the diazosulfonate in the entire layer to a labile form. The layer is then exposed to light of a second range of wavelengths through'a master which is transparent in its non-image regions. Light strikes the layer in areas corresponding to the non-image areas of the master and decomposes the labile form thereby eliminating the possibility of subsequent dye-formation. Then, by subjecting the layer to heat, the labile form remaining in the unexposed areas combines with the coupler to form a dyeimage.

In the second positive-working mode, the layer is exposed to light of both first and second ranges of wavelengths through a transparent master, thereby causing decomposition in the light-struck areas. Thereafter, the layer is illuminated overall with light of a first range of wavelengths and then subjected to heat, whereby the remaining diazosulfonate is converted to a labile form, which couples at the elevated temperature to form a dye image in the areas corresponding to the non-transparent areas of the master.

In the reversal mode, the layer is exposed image-wise to light of a first range of wavelengths, whereby in the areas struck by light, the diazosulfonate is converted to a labile form. Since the image is present but not visible, it maybe said that a latent image is formed in these areas. An azo dye is formed at the places struck by the light by heating the material so that the labile form combines with the coupling component. Thereafter, the background is cleared by exposing the light-sensitive layer to light at said first range of wavelengths and to light of a second range of wavelengths whereby the diazosulfonate in the non-imaged areas is destroyed.

In addition to the above-described photographic modes of copying, there exist in accordance with this invention a number of thermographic modes wherein imaging is accomplished by selectively heating the layer after exposing it overall to light of a first range of wavelengths at which the diazosulfonate is converted to a labile form. In one embodiment, the material of the invention is employed to thermographically copy an original containing an image which absorbs infrared radiation. As is known in the art, thermographic copying is effected by a number of arrangements of the original and copy material.

According to one such arrangement, the heat-sensitive layer is placed in direct contact with the image side of the original and exposed with heat rays directed through either the original or the copy material (which is transparent to infrared radiation). The image areas of the original absorb the infrared radiation and selectively heat the adjacent heat-sensitive layer of the copy material. In either case, a mirror-image copy is produced. In another arrangement, the image'side of the original is placed in heat-conductive contact with the surface of the copy material opposite the heat-sensitive side and infrared radiation is directed through either the copy material or the original. In the former case, the rayspass through the copy material and are selectively reflected (transmitted back) by the image on-the original. In the latter case, the rays are selectively absorbed by the image on the original and transmitted to the heat-sensitive layer. In these modifications, the heat-transparent copy support must be thin enough to permit readily the transmission of heat therethrough from the image to the heat-sensitive layer. In either case a directly readable copy is obtained. In yet another arrangement, the heat sensitive layer is placed in heat-conductive contact with the nonimage side of the original and radiation is directed through either the copy or original. In the former case, the rays pass through the copy material and are selectively reflected (transmitted back) by the image on the original. In the latter case, the rays are selectively absorbed by the image on the original and transmitted to the heat-sensitive layer. In these modifications, the original must be thin enough to permit readily the transmission of heat therethrough. In either case a mirror-image copy is obtained.

To clear the background areas, the material is exposed overall to actinic light of a second range of wavelengths which decomposes the uncoupled labile form of the diazosulfonate remaining in the layer.

In another embodiment, thermal energy is transferred directly to the layer by, for example, a heated stylus or a laser beam, the intensity of which is selectively modulated. By way of illustrating the latter, pictorial information gathered by a high-resolution television camera is recorded on the layer by using the camera output to modulate the laser beam. Alternatively, digital information from a computer is employed to modulate the beam. One advantage of this print-out process over present systems, for example, electrostatic methods, is that the image is formed immediately without the necessity of an additional toning or developing step. Fixing of the image is accomplished simply by exposing the layer overall to light of a second range of wavelengths whereby the residual labile form of the diazosulfonate is decomposed.

THE DIAZO COMPOUND The diazotype reproduction materials of the present invention comprise paper, film, or other suitable support carrying a light-activatable layer which includes an aryl diazosulfonate and a coupling component, preferably in an acid environment. The aryl diazosulfonate is typically incorporated as the alkali metal salt, quaternary ammonium salt, or the salt of an inorganic Lewis acid. The layer may further contain various additives to enhance the speed, density, and clearing behavior of the material.

As stated above, the preferred diazosulfonates of the invention exhibit a measurable spectral separation between said first and second ranges. Consequently, light of said first range of wavelengths does not affect the labile form. This is because said range consists essentially of wavelengths which convert diazosulfonate to the labile form and virtually none which cause decomposition. Compounds in this preferred class of diazosulfonates comprise benzene diazosulfonate and the following derivatives thereof; 2-methoxy; 2- phenoxy; 2-(4-methoxy) phenoxy; 2,4-dimethoxy; 2- methyl, 4-methoxy; 2,4-dimethyl; 2,4,6-trimethyl; 2,4,6-trimethoxy; 2,4-dimethoxy-5-chloro; 2-methoxy- S-nitro; 2-methoxy-S-acetamido; 2-methoxy-5-N,N- diethylsulfonamido; 2-methoxy-S-N-phenylcarbamyl; 2-methoxy-4-diazosulfonate-4'-methyl-diphenylsul-, fide; 3-methyl; 4-methyl; 4-methoxy; 4-ethoxy; 4-phenyl; 4phenoxy; 4-acetamido; 4-benzyloxy; and 3,4- ethylenedioxy benzene.

Although a number of other diazosulfonates have been found not to exhibit a measurable spectral separation between said first and second ranges, they do, however, produce a labile form when exposed to light. The difficulty is that the wavelengths at which the labile form is generated are very near to the wavelengths which cause the decomposition of the labile form. It has been found, nonetheless, that, as described above, by careful control .of the wavelengths of the imaging light, formation of the labile species can be favored over decomposition. Compounds in this latter category include meta-substituted benzene diazosulfonates such as 2,5-dimethoxy; 4,5-dimethoxy; 4-thioallyl, 5- methoxy; 2,5-diethoxy, 4-thioallyl; 2,5-diethoxy, 4- phenyl; 2,5-diethoxy, 4-(4-ethoxy) phenyl; 2,5- diethoxy, 4-phenoxy; 2-methoxy, 4,5-diphenoxy; and

-chloro; and many para-aminobenzene diazosulfonates, such as 4-(N-ethyl, N-benzyl)aminobenzene and 4-(N,N-diethyl) aminobenzene.

THE COUPLER ments which must be satisfied by the coupling component. For example, the component must be active in the azo-coupling reaction, but not so active as to cause premature production of the dye. It should be colorless and stable to light; it must not absorb radiation in the region which is actinic for the diazosulfonate and the labile form; and must not oxidize in air. Preferred couplers may be divided into the following groups, as

developed by Dinaburg, Photosensitive Diazo Compounds (1964) pp. 96-1 14. See also Kosar, Light-Sensitive Systems (1965) Table 6.2. Hydroxy compounds of the benzene series, particularly substituted phenols,

catechol and derivatives thereof, resorcinol and deriva- 2S tives thereof, hydroquinone derivatives, and trihydroxybenzenes; hydroxyand polyhydroxyv diphenyls; hydroxyand polyhydroxy compounds of the naphthalene series, including naphthoic acid derivatives; compounds containing active methylene groups,

THE ACID The diazo reproduction formulation of the invention provides an acidic environment for the diazosulfonate and coupler. This is ordinarily accomplished by the addition of an acid to the coating formulation, preferably a weak acid, e.g., an organic acid or an inorganic Lewis acid such as zinc or tin chloride. Less preferred are the strong inorganic acids and the sulfonate acids. Alternatively, an acidic environment is provided by making the substrate or matrix acid, or by a combination of both of the above techniques. The formulation is typically coated onto a substrate or matrix. The degree of acidity which mustbe supplied depends not only upon the diazosulfonate and coupler but on the matrix as well. Cellulose acetate, a common substrate for film is itself slightly acidic. Some couplers are bases, the alkalinity of which must be compensated for by acid. Other couplers are acid, and, as more fully described hereinafter, eliminate the need for further addition of acid.

3-dihydrox- 35 acid An organic acid most desirably, for use in the present invention has a pKa value of from greater than 1 to about 4, as measured in water. Generally, use of acids near the bottom of this range (having a pKa near 1) produces images of lesser density but with exceptionally clear background areas. Use of acids near the top of this range (having a pKa near 4) produces very dense images which may suffer from background coloration. Specifically preferred acids are benzenehexacarboxylic (mellitic); l,2,4,5- benzenetetracarboxylic; cis-l ,2-ethylenedicarboxylic (maleic); 1,2,4rbenzenetricarboxylic (trimellitic);

ortho-bromobenzoic; ortho-benzenedicarboxylic (phthalic); ortho-hydroxybenzoic (salicylic); trans-1,2- ethylenedicarboxylic (fumaric); 2-hydroxy-l,2,3- propanetricarboxylic (citric); 2-furoic (Z-furan carboxylic); chloroacetic; dichloroacetic; phenoxyacetic; ethoxyacetic; tartaric; and lactic.

In a further modification of the invention, the number of essential components is reduced to two by the use of a coupler which is an acid. Suitable examples include 2-hydroxy-3-naphthoic, 2-hydroxy-6-naphthoic, 2,6-dihydroxybenzoic, 2,4,6-trihydroxybenzoic, and cyanoacetic (malonic mononitrile).

Describing the invention now in greater detail, with respect to the preferred diazosulfonates, namely, those which exhibit measurable spectral separation, a layer of the reproduction material is activated by exposure to light of wavelengths greater than about 350 nm at a temperature which is conveniently room temperature but should be below F. When imaging is accomplished by light, coupling is promoted by raising the temperature of the layer to a temperature between 175 and 240 F for a time sufficient to develop the image therein. When imaging thermographically, heat is applied selectively to the layer for a time sufficient to produce an image of the density desired. Fixing is effected by exposing the layer at a temperature below 150 F to light having at least one wavelength less than about 350 nm and at least one greater than about 350 The principles, features and advantages of the invention will be further understood from a consideration of the following specific examples.

EXAMPLES l-V A light-sensitive coating formulation comprising the following components was prepared:

Each formulationwas bead-coated onto a cellulose diacetate substrate and dried at F (68 C) for four minutes.

The layer of diazosulfonate reproduction material produced from each formulation was then exposed through a partially opaque master at a temperature EXAMPLE VI A light-sensitive coating formulation comprising the following components was prepared:

Component Amount methanol 40 ml acetone 60 ml 2,4-dimethoxy benzene diazosulfonate, lithium salt 1.5 g phloroglucinol 0.5 g dichloroacetic acid 3.0 g

This formulation was bead-coated onto a polyester film (DuPonts Mylar) which had received an initial coating of cellulose acetate-butyrate, and dried at 155 F (68 C) for four minutes. The layer of diazosulfonate reproduction material was then exposed through a partially opaque master at a temperature below 150 F (66 C) for -20 seconds to light of wavelengths from 360 nm up to 430 nm at an intensity of about 0.1 wattlcm The reversal image was then developed by raising the temperature of the material to about 200 F (93 C) for 15-20 seconds. A sepia image of good density was obtained. The material was cooled to a temperature below 150 F and exposed for 30 seconds to light having at least one wavelength about 300 nm and at least one wavelength longer than about 360 nm at an intensity of 0.2 watt/cm to destroy the residual diazosulfonate, thereby fixing the image.

EXAMPLE VII EXAMPLE VIII A light-sensitive coating formulation comprising the following components was prepared:

Component Amount methanol 40 ml acetone 60 ml bxtwkneziaaefi 8 10 This formulation was bead-coated onto cellulose diacetate and dried. The resulting material was processed as in Example VI, producing a purple image.

EXAMPLES IX-XV A light-sensitive coating formulation comprising the following components was prepared:

Component Amount methanol 40 ml acetone 60 ml diacetoacet-ortho-dianisidide 1.5 g

. 4,8-dihydroxynaphthalene-l-sulfonic acid 0.5 g citric acid I 2.0 g diazosulfonate 2.0 g

selected from the group consistin of 2,5-diethoxy, 4-(4-ethoxy)phenyl enzene 2,5-diethoxy, 4-thiobenzylbenzene 2,5-diethoxy-4-diazosulfonate-4'-methyldiphenylsulfide 2,5-dimethoxy, 4-(4-methyl)phenylbenzene 2,5-dimethoxy, 4 (4-methoxy)phenylbenzene 2,5-diethoxy, 4-phenoxybenzene 2,5-diisopropoxy, 4-thioallylbenzene Each formulation was coated and processed as in Example VI. A black image was obtained, which was readily distinguished when viewed on a microfilm type of reader.

EXAMPLES XIV-XVIII A light-sensitive coating formulation comprising the following components was prepared:

selected from the group consisting of 2-hydroxy-6-methoxy-3-naphthanilide 2-hydroxy-6-methoxy-3-(2 -methyl)- naphthanilide 2-hydroxy-6-methox -3-(2',5'-dimethoxy-4'- chloro) naphthani ide Each formulation was coated and processed as in Example VI. An image of a blue shade was obtained.

EXAMPLES XIX-XXI A light-sensitive coating formulation comprising the following components was prepared:

dichloroacetic acid aceto acetanilide naphthanilidc (coupler) selected from the group consisting of 2-hydroxy-6-methoxy-3-naphthanilide 2-hydroxy-6-methoxy-3-(2-methyl)- naphthanilide 2-hydroxy-6-methoxy-3-(2',5'-dimethoxy-4- chloro) naphthanilide Each formulation was processed as in Example VI. A black image was obtained which was readily distinguished when viewed on a microfilm type of reader.

EXAMPLES XXII-XXIV A light-activatable coating formulation comprising the following components was prepared:

Component Amount methanol 40 ml acetone 60 ml 4-(N-ethyl, N-benzyl)aminobenzene diazosulfonate sodium salt 1.2 g a coupling component selected from the following acids: l.0 g

4,8-dihydroxynaphthalene-l-sulfonic acid 2,4 ,6-trihydroxybenzoic acid l-phenyl-B-carboxy-S-pyrazolone This formulation was bead-coated onto'a cellulose diacetate substrate and dried.

The layer of diazosulfonate reproduction material was then exposed through a partially opaque master at room temperature for 60 seconds to light from a mercury arc lamp filtered to exclude wavelengths shorter than 410 nm and at an intensity of about 0.1 watt/cm? The image was then developed by raising the temperature of the material to 200 F for 30 seconds. The material was cooled to a temperature below 150 F and exposed to unfiltered light from a mercury arc lamp for a time sufficient to decompose the remaining diazosulfonate, thereby fixing the image, which in the case of 4,8-dihydroxynaphthalene-l-sulfonic acid was a dense blue; of 2,4,6-trihydroxybenzoic acid was a dark brown; and of l-phenyl-3-carboxy-5-pyrazolone and was a dense magenta.

EXAMPLE xxv A light activatable coating formulation comprising the following components was prepared:

selected from the group consisting of: maleic, citric, dichloroacetic, salicylic. benzoic,, ethoxyacetic, phthalic This formulation was coated, and the resulting 2 EXAMPLE XXVI EXAMPLE XXVll A light-activatable coating formulation comprising the following components was prepared:

Component Amount methanol 40 ml acetone 60 ml l-[N(3-azabicyclo [3,2,2] nonane)] naphthalene-4- diazosulfonate, sodium salt 0.6 g 2,4,6-trihydroxybenzoic acid l.0 g

This formulation'was bead-coated onto a cellulose diacetate substrate and dried. The layer of diazosulfonate reproduction material was then exposed through a partially opaque master at a temperature below 150 F for seconds to light of wavelengths longer than 470 nm at an intensity of about 0.1 watt/cm. The image was then developed by raising the temperature of the material to about 200 F for l5-20 seconds. A purple image was obtained. The material was cooled to a temperature below F and exposed to light having at least one wavelength about 300 nm and at least one wavelength longer than 470 nm to destroy the residual diazosulfonate, thereby fixing the image.

EXAMPLE XXVIlI Diazosulfonate reproduction material according to Example VI was exposed overall at a temperature below 150 F (66 C) for l5-20 seconds to light of wavelengths longer than 360 nmat an intensity of about 0.1 watt/cm. The material was then exposed through a partially opaque master to light having at least one wavelength about 300 nm to destroy the labile form in the light-struck areas. A positive image was then developed by raising the temperature of the material to about 200 F (93 C) for 15-20 seconds. A sepia image of good density was obtained.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it is understood that various other changes and modifications thereof will occur to person skilled in the art without departing from the to a and scope of the invention as defined by the appended claims.

What'is claimed is:

l. The method of forming a reversal diazo image comprising:

a. image-wise exposing a layer of material which comprises, in an acidic environment, a salt of an aryl diazo-N-sulfonate, an azo coupling component, and-an organic acid having a pKa value of from greater than 1 to about 4, to light of wavelengths approximately equal to or greater than the absorption maximum of the diazo-N-sulfonate, whereby the diazo-N-sulfonate in the lightstruck areas of the layer is converted to a labile form which is substantially unaffected by light of the labile form, whereby the undeveloped diazo-N- sulfonate is converted to a labile form which in turn decomposed.

level and maintaining said level for a time sufficient to cause the labile form of the diazo-N-sulfonate remaining in the layer to combine with the azo coupling component to form an azo dye.

said wavelengths, 5; The method in accordance with claim 4 wherein raising the temperature of said layer to an elevated thtadiplzlo-N-suklxfonqte i? a benzene diazo-N-sulfonate.

level and maintaining said level for a time suffi- F F 0d or ormmg a posmve dlazo Image cient to cause the labile form to combine with the compl'lsmg' azo coupling component to form an azo dye in the lmagefwlse. exposnlg. a of material whlch areas struck by light during the image-wise expofi gl is g a i g gh ii 2 sure, said temperature and time being insufficient a y l u o 5 6 pl g o to cause any significant dye formation in those ponem and an ("game acld havmg pKa value of areas of the layer which were not struck by light from greater than 1 to about to light having at during theimage wise exposure and least one wavelength approximately equal'to or overall exposing said layer to light having at least giz ig gig2: i ggg g z gg ig gfg fpgiz:

one wavelen th a roximatel e ual to or reater than the abs rpti fi maximun i oi the diazo N-sulmately i g g thfan g g fi maximum 0 t e a ie orm o sai iazo- -su onate,

q p areas 15 converted to a labile form WhlCl'l IS in turn decomposed, b. exposing overall the layer to light of wavelengths approximately equal to or greater than the absorp- 2. The method in accordance with claim 1 wherein the diazo-N-sulfonate is a benzene diazo-N-sulfonate.

3. The method as claimed in claim 1 in which a. the image-wise exposure is at a temperature below 0 tion maximum of the diazo-N-sulfonate, whereby the remaining diazo-N-sulfonate is converted to a labile form, and

150 F to light of wavelengths greater than 350 the temperature of the layer is raised to between the overall exposure is at a temperature below 150 F to light having at least one wavelength less than 350 nm and at least one wavelength greater than 350 nm.

. raising the temperature of the layer to an elevated level and maintaining said level for a time sufficient to cause the labile form of the diazo-N-sulfonate remaining in the layer to combine with the azo coupling component to form an azo dye.

7. The method in accordance with claim 6 wherein the diazo-N-sulfonate is a benzene diazo-N -su1fonate.

8. The method of forming a reversal diazo image comprising:

4. The method of forming a positive diazo image comprising a. exposing overall a layer of material which comb.

labile form, image-wise exposing the layer to thermal radiation prises, in an acidic environment, a salt of an aryl diazo-N-sulfonate, an azo coupling component, and an organic acid having a pKa value of from greater than 1 to about 4, to light of wavelengths approximately equal to or greater than the absorption maximum of the diazo-N-sulfonate, whereby the diazo-N-sulfonate in the layer is converted to a labile form which is substantially unaffected by light of said wavelengths,

image-wise exposing the layer to light of wavelengths approximately equal to or less than the absorption maximum of the labile form, whereby the labile form in the light-struck areas of the layer is decomposed, and

c. raising thetemperature of the layer to an elevated sufficient to cause the labile form to combine with the azo coupling component to form an azo dye in the heated areas, said thermal radiation being insufficient to cause any significant dye formation in those areas of the layer which were protected from the thermal radiation by the image during said image-wise exposure, and

c. exposing the layer overall to light of wavelengths approximately equal to or less than the absorption maximum of the labile form, whereby the labile form of the diazo-N-sulfonate remaining in the layer is decomposed. t

9. The method in accordance with claim 8 wherein 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Page 3,713,825 Dated January 30, 1973 Inventofls) Eric Girard It is certified that error appears in the aboveddentified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 50, change "4phenoxy" to --4-phenoxy;-

Column 7, line 37, change "3,5,3',5'B-tetrahydroxy" to (3,5,3',5'tetrahydroxy Column .7, line 55, change "sulfonate" to -.sulfonic- Column 12, line 56, after "to" insert --a-- Column 12, line 57, delete "to a" and insert'therefor --spirit- Signed and Scaled this First Day of February 1977 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofParems and Trademarks 

1. The method of forming a reversal diazo image comprising: a. image-wise exposing a layer of material which comprises, in an acidic environment, a salt of an aryl diazo-N-sulfonate, an azo coupling component, and an organic acid having a pKa value of from greater than 1 to about 4, to light of wavelengths approximately equal to or greater than the absorption maximum of the diazo-N-sulfonate, whereby the diazo-N-sulfonate in the light-struck areas of the layer is converted to a labile form which is substantially unaffected by light of said wavelengths, b. raising the temperature of said layer to an elevated level and maintaining said level for a time sufficient to cause the labile form to combine with the azo coupling component to form an azo dye in the areas struck by light during the image-wise exposure, said temperature and time being insufficient to cause any significant dye formation in those areas of the layer which were not struck by light during the image-wise exposure, and c. overall exposiNg said layer to light having at least one wavelength approximately equal to or greater than the absorption maximum of the diazo-N-sulfonate and at least one wavelength approximately equal to or less than the absorption maximum of the labile form, whereby the undeveloped diazo-N-sulfonate is converted to a labile form which in turn decomposed.
 2. The method in accordance with claim 1 wherein the diazo-N-sulfonate is a benzene diazo-N-sulfonate.
 3. The method as claimed in claim 1 in which a. the image-wise exposure is at a temperature below 150* F to light of wavelengths greater than 350 nm, b. the temperature of the layer is raised to between 175* F and 240* F for a time sufficient to cause the labile form of the diazo-N-sulfonate to combine with the azo coupling component to form an azo dye in the areas struck by light during the image-wise exposure, but insufficient to cause any significant dye formation in those areas of the layer which were not struck by light during the image-wise exposure, and c. the overall exposure is at a temperature below 150* F to light having at least one wavelength less than 350 nm and at least one wavelength greater than 350 nm.
 4. The method of forming a positive diazo image comprising a. exposing overall a layer of material which comprises, in an acidic environment, a salt of an aryl diazo-N-sulfonate, an azo coupling component, and an organic acid having a pKa value of from greater than 1 to about 4, to light of wavelengths approximately equal to or greater than the absorption maximum of the diazo-N-sulfonate, whereby the diazo-N-sulfonate in the layer is converted to a labile form which is substantially unaffected by light of said wavelengths, b. image-wise exposing the layer to light of wavelengths approximately equal to or less than the absorption maximum of the labile form, whereby the labile form in the light-struck areas of the layer is decomposed, and c. raising the temperature of the layer to an elevated level and maintaining said level for a time sufficient to cause the labile form of the diazo-N-sulfonate remaining in the layer to combine with the azo coupling component to form an azo dye.
 5. The method in accordance with claim 4 wherein the diazo-N-sulfonate is a benzene diazo-N-sulfonate.
 6. The method for forming a positive diazo image comprising: a. image-wise exposing a layer of material which comprises, in an acidic environment, a salt of an aryl diazo-N-sulfonate, an azo coupling component, and an organic acid having a pKa value of from greater than 1 to about 4, to light having at least one wavelength approximately equal to or greater than the absorption maximum of the diazo-N-sulfonate and at least one wavelength approximately equal to or less than the absorption maximum of the labile form of said diazo-N-sulfonate, whereby the diazo-N-sulfonate in the light-struck areas is converted to a labile form which is in turn decomposed, b. exposing overall the layer to light of wavelengths approximately equal to or greater than the absorption maximum of the diazo-N-sulfonate, whereby the remaining diazo-N-sulfonate is converted to a labile form, and c. raising the temperature of the layer to an elevated level and maintaining said level for a time sufficient to cause the labile form of the diazo-N-sulfonate remaining in the layer to combine with the azo coupling component to form an azo dye.
 7. The method in accordance with claim 6 wherein the diazo-N-sulfonate is a benzene diazo-N-sulfonate.
 8. The method of forming a reversal diazo image comprising: a. exposing overall a layer of material which comprises, in an acidic environment, a salt of an aryl diazo-N-sulfonate, an azo coupling component, and an organic acid having a pKa value of from greater than 1 to about 4, to light of wavelengths approximateLy equal to or greater than the absorption maximum of the diazo-N-sulfonate, whereby the diazo-N-sulfonate in the layer is converted to a labile form, b. image-wise exposing the layer to thermal radiation sufficient to cause the labile form to combine with the azo coupling component to form an azo dye in the heated areas, said thermal radiation being insufficient to cause any significant dye formation in those areas of the layer which were protected from the thermal radiation by the image during said image-wise exposure, and c. exposing the layer overall to light of wavelengths approximately equal to or less than the absorption maximum of the labile form, whereby the labile form of the diazo-N-sulfonate remaining in the layer is decomposed. 